CCD sensors with multiple contact patterns

ABSTRACT

A pixel array in an image sensor includes multiple pixels. The pixel array includes vertical shift registers for shifting charge out of the pixel array. The vertical shift registers can be interspersed between the pixels, such as in an interline image sensor, or the photosensitive areas in the pixels can operate as vertical shift registers. The pixels are divided into blocks of pixels. One or more electrodes are disposed over each pixel. Conductive strips are disposed over the electrodes. Contacts are used to connect selected electrodes to respective conductive strips. The contacts in at least one block of pixels are positioned according to one contact pattern while the contacts in one or more other blocks are positioned according to a different contact pattern. The different contact patterns reduce or eliminate visible patterns in the contact locations.

TECHNICAL HELD

The present invention relates generally to image sensors for use indigital cameras and other types of image capture devices, and moreparticularly to Charge-Coupled-Device (CCD) image sensors.

BACKGROUND

A CCD image sensor typically includes an array of photosensitive areasthat collect charge carriers in response to light striking eachphotosensitive area. For an interline transfer sensor, the charge istransferred from the photosensitive areas to vertical shift registers.The vertical shift registers shift the charge in parallel one row at atime to a horizontal shift register. The horizontal shift register thenserially shifts the charge to an output circuit.

With a full frame transfer image sensor, the photosensitive areas alsooperate as vertical shift registers. The charge is shifted in parallelone row at a time from the vertical shift registers to the horizontalshift register. FIG. 1 is a simplified top view of a portion of a firstfull frame pixel array according to the prior art. Pixel array 100includes multiple photosensitive areas 102. Electrodes or gates 104, 106are disposed over the photosensitive areas in an alternating pattern. Toshift charge through the photosensitive areas, a vertical driving pulseV1 is applied to electrodes 104 and a vertical driving pulse V2 isapplied to electrodes 106. Typically the driving pulses V1, V2 areapplied at both ends of the electrodes 104, 106.

Typically electrodes 104 are formed by a first polysilicon layer andelectrodes 106 by a second polysilicon layer. Polysilicon is known tohave a relative high resistance. This high resistance causes thewaveforms of the driving pulses V1, V2 to deteriorate as the drivingpulses V1, V2 propagate away from the ends of the electrodes toward thecenter or middle (represented by line 108) of array 100. This problembecomes worse as the size of the array increases.

Several different techniques have been developed to address the issue ofsignal deterioration across electrodes. For example, U.S. Pat. No.5,194,751 includes a metal wiring layer that is connected to theelectrodes through contact regions. FIG. 2 is a simplified top view ofthis second prior art construction. Contact regions 200, 202, 204, 206between respective electrodes 208, 210, 212, 214 and the metal wiring216 are arranged in an orderly fashion throughout the array 218. Insteadof applying the driving pulses to the ends of the electrodes 208, 210,212, 214, the driving pulses are applied to the metal wiring layer 216.Thus, the driving pulses are applied to electrodes 208, 210, 212, 214 atthe various contact regions distributed throughout the array 218. Oneconcern with this design is that the orderly contact pattern issusceptible to detection by human eyes when a CCD image sensor isilluminated by a bright light. This is due to interaction between thecontacts between layers and the light.

Another concern is the density of contact regions 200, 202, 204, 206. Inrecent years, the trend of image sensor design is to increase the numberof pixels and to shrink the pixel size. This means contact regions 200,202, 204, 206 are formed closer together, increasing the probability foradjacent contact regions to short together. As shown in FIG. 2, eachpixel 220 in array 218 includes one contact region. Thus, in each row ofpixels, a contact region in one pixel 220 is immediately adjacent to,and diagonally offset from, the contact region in a neighboring pixel.This pattern can increase the percentage of—electrical shorts betweenelectrodes. Electrical shorts between the contact regions reduce themanufacturing yield of image sensors and increase the cost to produceimage sensors. On the other hand, if the density of the contact regionsis too sparse, the benefit of reduced signal deterioration decreasesbecause the driving pulses must propagate a greater distance betweencontact regions on each electrode.

FIG. 3 is a simplified top view of a portion of a third full frame imagesensor according to the prior art. Two electrodes 304, 306 are disposedover each pixel 302. Electrodes 304 are connected to metal strips 308via contacts 310, and electrodes 306 are connected to metal strips 312via contacts 314. The driving pulses are applied to pads 316, 318 and toelectrodes 304, 306 at the various contacts 310, 314 distributedthroughout the array 300. This reduces the propagation delays of thedriving pulses to the middle or center of the electrodes 304, 306.

As shown in FIG. 3, four adjacent metal strips are connected to the samepad 316, 318. This is an improvement over the FIG. 2 construction interms of reducing electrical shorts between adjacent contacts becauseany short between adjacent metal strips within the four strips is not anissue since the four strips are all connected to the same pad. Anotherfeature of the FIG. 3 design is that within each four-by-four (4×4)block 320 of pixels 302, the contacts within that block 320 areconnected to the same electrode. Pixel array 300 has only one contact toa respective electrode in each single row and each single column inblock 320 and any two contacts are not adjacent to each other. Byreducing the contact density, the FIG. 3 design reduces the frequency ofthe shorts. However, since each contact is placed diagonally acrosspixel array 300 (as shown by the three diagonal arrows), the pattern ofthe contacts in array 300 is still susceptible to detection by the humaneye when illuminated by bright light.

FIG. 4 is a simplified top view of a portion of a fourth full framepixel array in accordance with the prior art. Pixel array 400 includeselectrodes 402, 404 disposed over each pixel 406 in array 400. Contacts408, 410 connect respective electrodes 402, 404 to a metal strip (notshown in FIG. 4). All of the contacts 408 disposed in column group 412are connected to electrode 402, while the contacts 410 in column group414 are connected to electrode 404. Within each five-by-five block 416of pixels in column group 412, a contact 408 to electrode 402 is formedin row 1 and column 1; row 2 and column 4; row 3 and column 2; row 4 andcolumn 5; and row 5 and column 3. This pattern of contacts in block 416is fixed and repeats, or is tiled, across column group 412. The samecontact pattern is used for the contacts 410 to electrode 404 in columngroup 414 (see block 418). The two contact patterns produce a diagonalpattern of contacts that can be easily seen (shown by two diagonalarrows in pixel array 400). The contact patterns produce image artifactsin an image captured by pixel array 400 when the pixel array isilluminated under a bright light.

SUMMARY

A pixel array in an image sensor includes multiple pixels. The pixelarray includes vertical shift registers for shifting charge out of thepixel array. The vertical shift registers can be interspersed betweenthe pixels, such as in an interline image sensor, or the photosensitiveareas in the pixels can operate as vertical shift registers. The pixelsare divided into blocks of pixels. The blocks of pixels include two ormore pixels in one embodiment in accordance with the invention. One ormore electrodes are disposed over each pixel. Conductive strips aredisposed over the electrodes. Contacts are used to connect selectedelectrodes to respective conductive strips. The contacts in at least oneblock of pixels are positioned according to one contact pattern whilethe contacts in one or more other blocks are positioned according to adifferent contact pattern. The different contact patterns reduce oreliminate visible patterns in the contact locations.

One method for determining contact locations in a pixel array firstgroups all of the pixels in the pixel array into blocks of two or morepixels. Different contact patterns are then used in substantially all ofthe blocks. For example, in one embodiment in accordance with theinvention, a contact pattern is randomly generated for each block.

Another method for determining contact locations in a pixel array firstgroups a portion of the pixels in the pixel array into two or moreblocks of pixels. Different contact patterns are then used insubstantially all of the blocks. For example, in one embodiment inaccordance with the invention, a contact pattern is randomly generatedfor each block. The blocks, and the contact patterns contained therein,are then tiled over the entire pixel array.

And yet another method for determining contact locations in a pixelarray uses a first contact pattern for all of the contacts in the pixelarray. The first contact pattern can be any known or given contactpattern. The pixel array is then grouped into blocks of pixels. Blocklocations within the pixel array are selected and a different (second)contact pattern is used in the selected block locations. Each of theselected block locations can have a different contact pattern, or one ormore different contact patterns can be used in the selected blocklocations.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are better understood with reference to thefollowing drawings. The elements of the drawings are not necessarily toscale relative to each other.

FIG. 1 is a simplified top view of a portion of a first full frame pixelarray according to the prior art;

FIG. 2 is a simplified top view of a portion of a second full framepixel array according to the prior art;

FIG. 3 is a simplified top view of a portion of a third full frame pixelarray according to the prior art;

FIG. 4 is a simplified top view of a portion of a fourth full framepixel array according to the prior art;

FIG. 5 is a flowchart of a first method for determining locations forcontacts in a pixel array in an embodiment in accordance with theinvention;

FIG. 6 is a simplified top view of a portion of a pixel array in anembodiment in accordance with the invention;

FIG. 7 is a simplified top view of a portion of a first full frame pixelarray in an embodiment in accordance with the invention;

FIG. 8 is a simplified top view of a portion of a second full framepixel array in an embodiment in accordance with the invention;

FIG. 9 is a simplified top view of a portion of a third full frame pixelarray in an embodiment in accordance with the invention;

FIG. 10 is a simplified top view of a portion of a fourth full framepixel array in an embodiment in accordance with the invention;

FIG. 11 is a flowchart of a second method for determining locations forcontacts in a pixel array in an embodiment in accordance with theinvention;

FIG. 12 is a simplified top view of a portion of a pixel array in anembodiment in accordance with the invention;

FIG. 13 is a flowchart of a third method for determining locations forcontacts in a pixel array in an embodiment in accordance with theinvention; and

FIG. 14 is a simplified top view of a portion of a pixel array in anembodiment in accordance with the invention.

ADVANTAGEOUS EFFECTS

One advantage of the present invention is to make contact locations orpatterns in an image sensor pixel array less detectable under allillumination conditions. The present invention also reduces or minimizesthe risk of electrical shorts between contacts.

DETAILED DESCRIPTION

Throughout the specification and claims the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The meaning of “a,” “an,” and “the” includes pluralreference, the meaning of “in” includes “in” and “on.” The term“connected” means either a direct electrical connection between theitems connected or an indirect connection through one or more passive oractive intermediary devices. The term “circuit” means either a singlecomponent or a multiplicity of components, either active or passive,that are connected together to provide a desired function. The term“signal” means at least one current, voltage, or data signal.

Additionally, directional terms such as “on”, “over”, “top”, “bottom”,“left”, “right”, are used with reference to the orientation of theFigure(s) being described. Because components of embodiments of thepresent invention can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration only and is in no way limiting. When used in conjunctionwith layers of an image sensor wafer or corresponding image sensor, thedirectional terminology is intended to be construed broadly, andtherefore should not be interpreted to preclude the presence of one ormore intervening layers or other intervening image sensor features orelements.

Referring to the drawings, like numbers indicate like parts throughoutthe views.

FIG. 5 is a flowchart of a method for determining locations for contactsin a pixel array in an embodiment in accordance with the invention.Initially, the pixels in the pixel array are grouped into blocks ofpixels (block 500). In one embodiment in accordance with the invention,the blocks of pixels include two or more pixels. The number of pixels ineach block is based on the number of pixels in the pixel array, thesheet resistances of the electrodes and conductive strips, and thetargeted driving pulse width in an embodiment in accordance with theinvention. Additionally, the blocks can be configured in any givenarrangement or orientation. The pixels in each block can be arranged ina square configuration, a rectangular configuration, or any other shapeor arrangement.

Next, as shown in block 502, different contact patterns are generatedfor the contacts in all of the blocks, or in substantially all of theblocks. The contact pattern in a portion of the blocks (one or moreblocks) should differ from the contact pattern for at least one otherdiscrete portion of blocks (one or more blocks).

Each contact pattern is randomly generated using a program running on acomputing device in an embodiment in accordance with the invention.Other embodiments in accordance with the invention can produce thedifferent contact patterns using alternate techniques. For example, thedifferent contact patterns can include a collection of known differentcontact patterns that are assigned to the respective blocks in theportion of the pixel array.

In a pixel array having rows and columns of pixels, the followingprinciples govern the generation of contact locations in the blocks inan embodiment in accordance with the invention. Inside each block, atany given row of pixels, only a single electrode in one pixel isconnected to a conductive strip by a contact. Inside each block, at anygiven column of pixels, only a single electrode in one pixel isconnected to a conductive strip by a contact. Inside a block, thecontacts are separated by at least one pixel. Inside the blocks that areimmediately adjacent to one another vertically, the same electrodes areconnected to a conductive strip by a contact. Inside the blocks that areimmediately adjacent to one another horizontally, alternate electrodesare connected to conductive strips by contacts. And finally, thecontacts within the blocks and between neighboring blocks are separatedfrom each other by at least one pixel. Other embodiments in accordancewith the invention can use additional principles, or differentprinciples from the described principles, or no principles whendetermining the contact locations in the pixel array.

Because the contact patterns are randomly generated, one or more contactpatterns may match or be duplicates of each other. Thus, differentcontact patterns may not be generated for all of the blocks in the pixelarray, but rather for substantially all of the blocks.

FIGS. 6-10, 12, and 14 illustrate alternate implementations of pixelarrays in embodiments in accordance with the invention. Eachimplementation is described as having a given number of electrodesdisposed over each pixel and a certain number of pixels in the blocks ofpixels. Other embodiments in accordance with the invention, however, arenot limited to these specifications. A pixel array can dispose anynumber of electrodes over each pixel. By way of example only, a pixelarray can provide one or four electrodes over each pixel.

Similarly, a pixel array can include any number of pixels in each blockof pixels. And the blocks can be configured into any given shape ororientation. For example, a block of pixels can be arranged in a squareor rectangular shape.

Referring now to FIG. 6, there is shown a simplified top view of aportion of a pixel array in an embodiment in accordance with theinvention. Pixel array 600 includes two electrodes 602, 604 disposedover each pixel 606. Contacts 608, 610 are used to connect respectiveelectrodes 602, 604 to conductive strips (not shown in FIG. 6). All ofthe contacts 608 in column groups 612, 614 are connected to electrode602, while the contacts 610 in column group 616 are connected toelectrode 604.

The portion of pixel array 600 shown in FIG. 6 includes fifteen rows andfifteen columns of pixels 606. The pixels 606 are grouped into blocks oftwenty-five pixels (five rows of pixels by five columns of pixels, or5×5 blocks). Thus, the portion shown in FIG. 6 includes a total of nine5×5 blocks. The contact patterns used in the blocks are randomlygenerated for each block. For example, in block 618 in column group 612,electrodes 602 are connected to conductive strips in row 1 and column 5;row 2 and column 2; row 3 and column 4; row 4 and column 1; and row 5and column 3. In block 620 in the same column group 612, electrodes 602are connected to conductive strips in row 6 and column 5; row 7 andcolumn 3; row 8 and column 1; row 9 and column 4; and row 10 and column2.

In block 622 in column group 614, electrodes 602 are connected toconductive strips in row 1 and column 13; row 2 and column 15; row 3 andcolumn 12; row 4 and column 14; and row 5 and column 11. As shown inFIG. 6, the contact patterns in blocks 618, 620, 622 are different fromeach other.

Within column group 616, electrodes 604 in block 624 are connected toconductive strips in row 11 and column 8; row 12 and column 6; row 13and column 9; row 14 and column 7; and row 15 and column 10. Note thatin the same column group 616, the contact pattern in block 624 differsfrom the contact pattern in block 626. Moreover, all of the contactpatterns in blocks 618, 620, 622, 624 and 626 differ from each other.The random contact patterns reduce or eliminate visible patterns thatcan be detected easily by the human eye.

Additionally, across pixel array 600, all of the contacts are separatedfrom each other by at least one pixel. This separation improvesmanufacturing yields because the risk of electrical shorts betweencontacts is reduced or eliminated.

FIG. 7 is a simplified top view of a portion of a first full frame pixelarray in an embodiment in accordance with the invention. Pixel array 700includes two electrodes 702, 704 disposed over each pixel 706. Eachcontact 708 in column group 710 is connected to electrode 702 andconductive strip 712, while each contact 714 in column group 716 isconnected to electrode 704 and conductive strip 718.

Conductive strips 712, 718 are disposed over electrodes 702, 704.Conductive strips 712, 718 are uniform and extend across pixel array700. Conductive strips 712, 718 are disposed substantially perpendicularto electrodes 702, 704 in an embodiment in accordance with theinvention. Other embodiments in accordance with the invention candispose the conductive strips over the electrodes with a differentorientation with respect to the electrodes.

The portion of pixel array 700 shown in FIG. 7 includes eight rows andeight columns of pixels 706. The pixels are grouped into 4×4 blocks ofpixels. Thus, the portion includes a total of four 4×4 blocks 736 ofpixels. The contact patterns in the four blocks differ from one another.The different contact patterns reduce or eliminate visible patterns thatcan be detected easily by the human eye. The contact pattern in eachblock is randomly generated using a software program running on acomputing device in an embodiment in accordance with the invention.Other embodiments in accordance with the invention can determine thedifferent contact patterns using alternate techniques.

Bus lines 720, 726 are formed along the periphery of pixel array 700.Conductive strips 712 are connected to bus line 720 via contacts 722.Bus line 720 is connected to bond pad 724. Both ends of electrodes 702are connected to bus line 720 via contacts 738.

Similarly, conductive strips 718 are connected to bus line 726 viacontacts 728. Bus line 726 is connected to bond pad 730. Both ends ofelectrodes 704 are connected to bus line 726 via contacts 740. Thedriving pulses applied to bond pads 724, 730 are transmitted toelectrodes 702, 704, respectively, from both left and right ends of theelectrodes via contacts 738, 740, as well as from contacts 708, 714 toconductive strips 712, 718. The driving pulses are used to shift ortransfer charge out of pixel array 700 (on a row-by-row basis) tohorizontal shift register 732. Horizontal register 732 then seriallyshifts the charge to output circuit 734.

Conductive strips 712, 718 are made of metal and electrodes 702, 704 ofpolysilicon in an embodiment in accordance with the invention. Thedegradation of the driving pulse waveforms is reduced because the sheetresistance of the metal conductive strips is smaller than the sheetresistance of the polysilicon.

Referring now to FIG. 8, there is shown a block diagram of an imagesensor 800 in another embodiment in accordance with the invention. Theembodiment illustrated in FIG. 8 is similar to the embodiment depictedin FIG. 7 except that both ends of electrodes 702, 704 are connected tobus lines 720, 726 by conductive strips 800, 802, respectively.

Conductive strips 800, 802 are made of a metal in an embodiment inaccordance with the invention. Conductive strips 800, 802 are disposedsubstantially perpendicular to electrodes 702, 704 in the illustratedembodiment. Other embodiments in accordance with the invention candispose the conductive strips over the electrodes with a differentorientation with respect to the electrodes.

Electrodes 702 are connected to conductive strip 800 via contacts 804.Conductive strip 800 is connected to bus line 720 via contacts 806.Similarly, electrodes 704 are connected to conductive strips 802 viacontacts 808. Conductive strips 802 are connected to bus line 726 viacontacts 810.

Since conductive strips 712, 718, 800, 802 can be made from the samematerial, the pixels in the center of array 812 and at both ends of thearray 812 have relatively the same electrical properties like resistanceand capacitance.

FIG. 9 is a simplified top view of a portion of a third full frame pixelarray in an embodiment in accordance with the invention. Image sensor900 has four output circuits 902, 904, 906, 908. Two electrodes 910, 912are disposed over each pixel 914. In the lower left quadrant of imagesensor 900, electrodes 910 are connected to conductive strips 916 viacontacts 918. Conductive strips 916 are electrically connected to bondpad 920 via contacts 922. To simplify the drawing, only one contact 918is shown. The charge can be transferred to either horizontal register924 or horizontal register 926, depending on the clocking signalsapplied to bond pads 920, 928, 930, 932.

Similarly, in the lower right quadrant of pixel array 900, electrodes912 are connected to conductive strips 934 via contacts 936. Conductivestrips 934 are electrically connected to bond pad 938 via contacts 940.Again, only one contact 936 is shown in the figure. The charge in thelower right quadrant of pixel array 900 can be transferred to eitherhorizontal register 942 or horizontal register 944.

In the FIG. 9 embodiment, bond pads 920, 946 are connected together andbond pads 928, 938 are connected together. One advantage to thisconstruction is the waveform degradation of the driving pulses isreduced because the driving pulses are applied to the bond pads fromboth sides of pixel array 900.

The upper left quadrant in pixel array 900 connects electrodes 910 toconductive strips 948 via contacts 950. Conductive strips 948 areconnected to bond pad 932 via contacts 952. The upper right quadrant inpixel array 900 connects electrodes 912 to conductive strips 954 viacontacts 956. Conductive strips 954 are connected to bond pad 958 viacontacts 960. Bond pads 932, 962 are connected together and bond pads930, 958 are connected together.

Conductive strips 916, 934, 948, 954 are disposed over electrodes 910,912. Conductive strips 916, 934, 948, 954 extend over only portions ofpixel array 900. Conductive strips 916, 934, 948, 954 are disposedsubstantially perpendicular to electrodes 910, 912 in an embodiment inaccordance with the invention. Other embodiments in accordance with theinvention can dispose the conductive strips over the electrodes with adifferent orientation with respect to the electrodes.

Conductive strips 916, 948 are not connected to each other, andconductive strips 934, 954 are not connected to each other. Bond pads920, 928, 930, 932 are not connected together, and bond pads 938, 946,958, 962 are not connected together. A gap 964 physically exists betweenthe conductive strips 948, 954 in the upper quadrants and the conductivestrips 916, 934 in the lower quadrants. Gap 964 allows the chargetransfer to be bi-directional using techniques known in the art. Chargein pixel array 900 can be read out to one output circuit 902, 904, 906,or 908, to two output circuits 902 and 904, 906 and 908, 902 and 908, or904 and 906, or to all four output circuits 902, 904, 906, 908. Thedirection of charge transfer through pixel array 900 depends on thewaveforms of the driving pulses transmitted to the electrodes in eachquadrant. The direction of charge transfer through the horizontalregisters 926, 944 and horizontal registers 924, 942 depends on thewaveforms of the horizontal driving pulses applied to the distinctelectrodes (not shown) disposed over the horizontal registers.

Referring now to FIG. 10, there is a simplified top view of a portion ofa fourth full frame pixel array in an embodiment in accordance with theinvention. Pixel array 1000 has two electrodes 1002, 1004 disposed overeach pixel 1006. Conductive strips 1008, 1010, 1012, 1014 are disposedover electrodes 1002, 1004. Conductive strips 1008, 1010, 1012, 1014 andare uniform and extend across pixel array 1000. Conductive strips 1008,1010, 1012, 1014 are disposed substantially perpendicular to theelectrodes in the illustrated embodiment. Other embodiments inaccordance with the invention can dispose the conductive strips over theelectrodes with a different orientation with respect to the electrodes.

The center of pixel array 1000 is indicated by a dash line 1016. Theconnections between electrodes 1002, 1004 and conductive strips 1008,1010, 1012, 1014 are implemented to allow for bi-directional readout ofpixel array 1000. For clarity, only a limited number of contacts areshown in FIG. 10. Electrodes 1002 located in the lower half of pixelarray 1000 are connected to conductive strips 1008 via contacts 1018. Inthe upper half of pixel array 1000, electrodes 1002 are connected toconductive strips 1010 via contacts 1020. There are no contacts betweenelectrodes 1002 and conductive strips 1008 in the upper half of pixelarray 1000 and there are no contacts between electrodes 1002 andconductive strips 1010 in the lower half of pixel array 1000.

Electrodes 1004 located in the lower half of pixel array 1000 areconnected to conductive strips 1014 via contacts 1022. In the upper halfof pixel array 1000, electrodes 1004 are connected to conductive strips1012 via contacts 1024. There are no contacts between electrodes 1004and conductive strips 1014 in the upper half of pixel array 1000 andthere are no contacts between electrodes 1004 and conductive strips 1012in the lower half of pixel array 1000.

Conductive strips 1008 are connected to bond pad 1042 via contacts 1044.Conductive strips 1010 are connected to bond pad 1046 via contacts 1048.Conductive strips 1012 are connected to bond pad 1050 via contacts 1052.And conductive strips 1014 are connected to bond pads 1054 via contacts1056. Bond pads 1050 are not connected to bond pads 1054.

Charge in pixel array 1000 can be read out to one output circuit 1026,1028, 1030, or 1032, to two output circuits 1026 and 1028, 1030 and1032, 1026 and 1032, or 1028 and 1030, or to all four output circuits1026, 1028, 1030 or 1032. The direction of charge transfer through pixelarray 1000 depends on the waveforms of the driving pulses transmitted tothe electrodes 1002, 1004. The direction of charge transfer through thehorizontal registers 1034, 1036 and horizontal registers 1038, 1040depends on the waveforms of the horizontal driving pulses applied to thedistinct electrodes (not shown) disposed over the horizontal registers.The arrangement eliminates the gap in the middle shown in FIG. 9.

FIG. 11 is a flowchart of a second method for determining locations forcontacts in a pixel array in an embodiment in accordance with theinvention. Initially, a portion of a pixel array is grouped into blocksof pixels (block 1100). The blocks of pixels can include any number ofpixels and be configured in any given shape or orientation. The numberof blocks of pixels produced in block 1100 depends on the number ofpixels in the pixel array, the number of pixels in each block, the sheetresistances of the electrodes and conductive strips, and the targeteddriving pulse width in an embodiment in accordance with the invention.

A different contact pattern is then produced for the contacts in eachblock, or for the contacts in substantially each block, as shown inblock 1102. The contact patterns are randomly generated using a softwareprogram running on a computing device in an embodiment in accordancewith the invention. Other embodiments in accordance with the inventioncan generate the different contact patterns using alternate techniques.For example, the different contact patterns can be selected from variousknown contact patterns in another embodiment in accordance with theinvention.

If the contact patterns are randomly generated, one or more contactpatterns may match or be duplicates of each other. Thus, differentcontact patterns may not be generated for all of the blocks in theportion of the pixel array, but rather for substantially all of theblocks.

Next, as shown in block 1104, the blocks are tiled, or repeatedly usedin an ordered placement, over the entire array. The different contactpatterns reduce or eliminate visible patterns that can be detectedeasily by the human eye.

Referring now to FIG. 12, there is shown a simplified top view of aportion of a pixel array in an embodiment in accordance with theinvention. Pixel array 1200 includes multiple pixels 1202 with twoelectrodes 1204, 1206 disposed over each pixel 1202. For simplicity,only two electrodes are illustrated in the figure. The pixels in region1208 are divided into blocks 1210 of pixels 1202. For simplicity, thepixels have been divided into four blocks 1210 each block including atotal of sixteen pixels (4 rows of pixels by 4 columns of pixels).

In each block 1210, different contact patterns are utilized for thecontacts (not shown in FIG. 12) between the electrodes 1204, 1206 andconductive strips (not shown in FIG. 12). All of the contact patterns inregion 1208 are then tiled over the entire pixel array 1200. Thedifferent contact patterns reduce or eliminate visible patterns that canbe detected by the human eye.

FIG. 13 is a flowchart of a third method for determining locations forcontacts in a pixel array in an embodiment in accordance with theinvention. Initially, as shown in block 1300, a first contact pattern isutilized for the contacts between the electrodes and conductive strips.The first contact pattern can be any known or given contact pattern.

The pixels in the pixel array are then grouped into blocks, as shown inblock 1302. Next, as shown in block 1304, select block locations withinthe pixel array are randomly determined in an embodiment in accordancewith the invention. Other embodiments can determine block locationsusing alternate techniques. For example, the block locations can beestablished based on the locations of image artifacts produced by thefirst contact pattern.

One or more different contact patterns are then used in the blockslocated at the randomly determined block locations (block 1306). Thedifferent contact patterns can be randomly generated for each block orfor some of the blocks, or any known contact pattern or patterns can beused in the blocks.

The first contact pattern in the select block locations is replaced witha different contact pattern (block 1308). The number of blocks, thenumber of pixels in each block, and the number of select block locationsdepend on the number of pixels in the pixel array, the number of pixelsin each block, the sheet resistances of the electrodes and conductivestrips, and the targeted driving pulse width in an embodiment inaccordance with the invention.

Referring now to FIG. 14, there is shown a simplified top view of aportion of a pixel array in an embodiment in accordance with theinvention. Pixel array 1400 includes blocks 1402 of pixels. A first orknown contact pattern (not shown in FIG. 14) is used in pixel array1400. Select block locations 1404 are determined and a different contactpattern (not shown) is for the contacts (not shown in FIG. 14) betweenthe electrodes and conductive strips (not shown in FIG. 14) in theselect block locations. The different contact patterns in the selectblock locations 1404 reduce or eliminate visible patterns that can bedetected easily by the human eye.

In summary, embodiments of the invention utilize two or more differentcontact patterns across a pixel array for contacts between selectedelectrodes and respective conductive strips. The two or more differentcontact patterns are intermingled or mixed together to reduce oreliminate the visible patterns that can be detected by the human eye.The different contact patterns can be used to break up or disperse someor all of the visible contact patterns. The different contact patternscan result in a non-uniform pattern of contacts for portions of thearray or for the entire array, an unpredictable pattern of contacts forportions of the array or for the entire array, or a non-tileable patternof contacts for portions of the array or for the entire array.

The contact locations can be separated from each other by at least onepixel. When the pixel array is configured in rows and columns, at anygiven row of pixels, only one pixel can include a contact between asingle electrode and a conductive strip. At any given column of pixels,only one pixel can include a contact between a single electrode and aconductive strip. Inside the blocks, contacts can be provided betweenthe conductive strips and the same electrodes.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. Additionally, even though specific embodiments of theinvention have been described herein, it should be noted that theapplication is not limited to these embodiments. In particular, anyfeatures described with respect to one embodiment may also be used inother embodiments, where compatible. And the features of the differentembodiments may be exchanged, where compatible. For example, in FIG. 10,instead of having only one conductive strip connected at the bottom ofthe pixel array and one conductive strip connected at the top, otherembodiments in accordance with the invention can connect two or moreconductive strips to the same electrode from the bottom and twoconductive strips to same electrode from the top.

Parts List

-   100 pixel array-   102 photosensitive area-   104 electrode-   106 electrode-   108 line representing center of pixel array-   200 contact-   202 contact-   204 contact-   206 contact-   208 electrode-   210 electrode-   212 electrode-   214 electrode-   216 metal wiring-   218 pixel array-   220 pixel-   300 pixel array-   302 pixel-   304 electrode-   306 electrode-   308 metal strip-   310 contact-   312 metal strip-   314 contact-   316 bond pad-   318 bond pad-   320 block of pixels-   400 pixel array-   402 electrode-   404 electrode-   406 pixel-   408 contact-   410 contact-   412 column group-   414 column group-   416 block of pixels-   418 block of pixels-   600 pixel array-   602 electrode-   604 electrode-   606 pixel-   608 contact-   610 contact-   612 column group-   614 column group-   616 column group-   618 block of pixels-   620 block of pixels-   622 block of pixels-   624 block of pixels-   626 block of pixels-   700 pixel array-   702 electrode-   704 electrode-   706 pixel-   708 contact-   710 column group-   712 conductive strip-   714 contact-   716 column group-   718 conductive strip-   720 bus line-   722 contact-   724 bond pad-   726 bus line-   728 contact-   730 bond pad-   732 horizontal shift register-   734 output circuit-   736 block of pixels-   738 contact-   740 contact-   800 conductive strip-   802 conductive strip-   804 contact-   806 contact-   808 contact-   810 contact-   812 pixel array-   900 pixel array-   902 output circuit-   904 output circuit-   906 output circuit-   908 output circuit-   910 electrode-   912 electrode-   914 pixel-   916 conductive strip-   918 contact-   920 bond pad-   922 contact-   924 horizontal shift register-   926 horizontal shift register-   928 bond pad-   930 bond pad-   932 bond pad-   934 conductive strip-   936 contact-   938 bond pad-   940 contact-   942 horizontal shift register-   944 horizontal shift register-   946 bond pad-   948 conductive strip-   950 contact-   952 contact-   954 conductive strip-   956 contact-   958 bond pad-   960 contact-   962 bond pad-   964 gap-   1000 pixel array-   1002 electrode-   1004 electrode-   1006 pixel-   1008 conductive strip-   1010 conductive strip-   1012 conductive strip-   1014 conductive strip-   1016 dashed line representing middle of pixel array-   1018 contact-   1020 contact-   1022 contact-   1024 contact-   1026 output circuit-   1028 output circuit-   1030 output circuit-   1032 output circuit-   1034 horizontal shift register-   1036 horizontal shift register-   1038 horizontal shift register-   1040 horizontal shift register-   1042 bond pad-   1044 contact-   1046 bond pad-   1048 contact-   1050 bond pad-   1052 contact-   1054 bond pad-   1056 contact-   1200 pixel array-   1202 pixel-   1204 electrode-   1206 electrode-   1208 region-   1210 block-   1400 pixel array-   1402 block-   1404 selected block locations-   V1 driving pulse-   V2 driving pulse

What is claimed is:
 1. A method for determining, in a pixel arraycomprising (i) a plurality of pixels, one or more electrodes disposedover each pixel, and (iii) a plurality of conductive strips disposedover the electrodes, locations of contacts each connecting an electrodewith a conductive strip, the method comprising: providing the pixelarray, the plurality of pixels being organized as blocks of pixels, eachblock comprising a plurality of pixels; randomly selecting a subset ofblocks interspersed within the array, a plurality of blocks remainingunselected; providing a first contact pattern in each unselected blockof the array; and in each selected block of the array, providing acontact pattern different from the first contact pattern, therebyreducing or eliminating image artifacts arising due to contacts arrangedin the first contact pattern.
 2. The method as in claim 1, wherein thepixel array is arranged in a plurality of rows and columns.
 3. Themethod as in claim 2, wherein each block comprises a plurality of rowsof pixels, and for each row of pixels within a block, (i) one or more ofthe electrodes disposed over each pixel in the array extend over the rowof pixels, and (ii) the row comprises only one contact between eachelectrode extending over the row and a conductive strip.
 4. The methodas in claim 1, wherein each block of pixels comprises at least 16pixels.
 5. The method as in claim 1, wherein each block of pixelscomprises at least 25 pixels.